Power catamarans may provide a number of advantages in a variety of applications and have become quite common. Depending on the intended use, some catamarans are designed to have high speed planing capability. Planing generally can be described as the action of a boat in motion when it lifts hydrodynamically and skims along the water surface. In order for a boat to plane, it must leave its stern wave behind and rise up over its bow wave. A common acknowledged definition of planing is based on the speed/length ratio, that planing occurs when the speed of the boat divided by the square root of its water line length is equal to or is greater than 2.0. A number of hydrodynamic variables come into play when planing, including the relationship between lift and drag, the angle of incidence of the planing surfaces to the water surface (the planing angle), the beam-to-length proportions of the hull (aspect ratio) and the bottom loading (boat weight per planing area).
A catamaran typically has certain advantages over a monohull of similar displacement or weight. Generally, the catamaran provides a wider deck space, improved lateral stability and may be considered to provide a more comfortable ride.
The conventional split-V planing catamaran is constructed so that its hulls plane on their outwardly facing bottom surfaces. At planing speeds, the majority of the water is displaced outwardly and downwardly while a certain amount of water is induced upwardly on the inside substantially vertical surfaces of each hull. The water that is displaced upwardly between the hulls contributes very little to the hydrodynamic lift but adds significantly to the overall drag of the hull. Such a hull, with adequate propulsion power to generate enough hydrodynamic lift to raise the center bridging supports and hull sides clear of the water may be considered to be acceptable up to moderate sea conditions. When carrying heavy loads, however, the performance, handling characteristics and comfort of the conventional split-V planing catamaran are significantly diminished due in part to the substantially increased wetted surface, the heavy bottom area loading and the effect of waves slamming against the underside of the transverse bridging structure between the hulls. While these difficulties might be reduced with a lightweight, high powered catamaran, such a catamaran may present severe control problems at high speeds because the air pressure on the underside of the bridging structure may cause the craft to become airborne, with its bow high and touching down on its transom. In an extreme case, a backward flip can result. In general, the performance and handling of a conventional split-V type of catamaran is very sensitive to weight.
Also among the characteristics of conventional split-V planing catamaran hulls is that they do not bank well and, therefore, tend to skid in high speed turns. They also may present difficulties in steering control when encountering quartering or cross waves. A further difficulty that may be encountered with conventional powered catamaran designs is that they may develop more of a wake than is desirable at low speeds.
It is among the general objects of the invention to provide an improved power planing catamaran hull configuration that provides improved performance in the foregoing and other respects.